Operating mechanisms and method for slidable-gate closures

ABSTRACT

A mechanism for operating slidable gate closures on a bottompour vessel. The gates are individual blanks for closing the nozzle in the bottom of the vessel, or orifice gates for permitting pouring. Initially, the blank is positioned in line with the nozzle, while the orifice gate is supported temporarily in the space between the blank and a gate-pulling means. Gates can be loaded into this space without interference from the propelling means, which is located at the opposite side of the vessel. To start pouring, the two gates are pulled toward the propelling means to align the orifice gate with the nozzle and displace the blank. In one embodiment the two gates later can be pushed back along rails to return the blank into alignment with the nozzle to stop pouring, and the orifice gate can be removed or replaced without changing the blank. In another embodiment each time a new gate is pulled into alignment with the nozzle, the displaced gate drops from the mechanism.

[ Dec. 18, 1973 United States Patent [191 Shapland, Jr.

OPERATING MECHANISMS AND Primary ExaminerRobert B. Reeves METHODS FOR SLIDABLE-GATE Assistant Examiner-David A. Scherbel CLOSURES Attorney-Walter P. Wood Earle P. Shapland, Jr., Champaign, Ill.

[75] Inventor:

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

bottom-pour vessel. The gates are individual blanks for closing the nozzle in the bottom of the vessel, or orifice gates for permitting pouring. Initially, the blank [22] Filed: Feb. 23, 1972 is positioned in line with the nozzle, while the orifice [21 1 Appl' 228597 gate is supported temporarily in the space between the Related US. A li ti n D t blank and a gate-pulling means. Gates can be loaded [63] continuatiommpan of Ser- 74,785, SepL 23, into this space without interference from the propelling means, which IS located at the opposite side of the vessel. To start pouring, the two gates are pulled toward the propelling means to align the orifice gate with the nozzle and displace the blank. In one embodiment the two gates later can be pushed back along rails to return the blank into alignment with the nozzle to stop pouring, and the orifice gate can be removed or replaced without changing the blank. ln another [56] References Cited UNITED STATES PATENTS embodiment each time a new gate is pulled into alignment with the nozzle, the displaced gate drops from 3.613965 lO/l97l Shapland 222/512 X the mechanism 3,6l8,834 ll/l97l Shapland et al. 222/5l2 X 23 Claims, 8 Drawing Figures PATENTEDUEC 18 ms 3.779.42A sum 2 U? a 35 INVENTOR EARL P. SHAPLA/VD, Jr.

his A/forney PATENTEB-UEC 18 975 SHEET 30F 3 OPERATING MECHANISMS AND METHODS FOR SUITABLE-GATE CLOSURES This application is a continuation-in-part of my earlier US. Pat. application Ser. No. 74,785 filed Sept. 23, 1970.

This invention relates to improved operating mechanisms for slidable gates used to control flow of liquid from a bottom-pour vessel, and to improve flowcontroling methods.

Although my invention is not thus limited, my mechanisms and methods are particularly useful when applied to a vessel from which liquid metal is poured. An earlier patent granted to James T. Shapland, U.S. Pat. No. 3,352,465, shows a bottom-pour vessel which has a slidable gate closure supported on two rows of rocker arms (i.e., levers of the first class) pivoted to its bottom wall alongside opposite edges of the gate. Compression springs urge the outboard ends of the rocker arms downwardly, while the inboard ends bear upwardly against the gate. The springs allow the arms to yield as the gate undergoes thermal expansion and contraction. In one embodiment in which the gate can reciprocate, different portions of its area are solid to close an outlet nozzle in the bottom wall of the vessel, or provide an orifice to be aligned with the nozzle to permit pouring. In another embodiment, which usually is preferred, the gates are of the slide-through type. Different gates either are blanks for closing the nozzle or have orifices for pouring. As each gate is pushed into line with the nozzle, it displaces the preceding gate. In both embodiments a fluid-pressure cylinder is mounted on the bottom of the vessel for propelling the gates. In the slidethrough embodiment the displaced gate is pushed in a direction away from the propelling means.

An object of my invention is to provide improved gate-operating mechanisms and methods which utilize separate blank and orifice gates, but in which the gates can reciprocate, whereby I avoid the need for installing a new gate every time I open or close the outlet of the vessel.

A further object is to provide improved gateoperating mechanisms and methods in which new gates are pulled rather than pushed into line with the outlet of a vessel, displacing the preceding gate toward the propelling means.

A further object is to provide gate-operating mechanisms which enable an orifice gate to be removed and replaced at any time when the outlet is closed with a blank without disturbing the blank.

A further object is to provide improved gateoperating mechanisms wherein new gates are loaded into the mechanism from an operators station without interference by the propelling means, which is at the opposite side of the vessel from the operator.

In the drawings:

FIG. I is a longitudinal sectional view of a portion of a bottom-pour vessel which is equipped with one embodiment of my improved gate-operating mechanism, the view being taken on line II of FIG. 2;

FIG. 2 is a horizontal section on line II-II of FIG. I;

FIG. 3 is a cross-section on line IIIIII of FIG. 1;

FIG. 4 is a cross-section on line IV-IV of FIG. 1;

FIG. 5 is a longitudinal section similar to FIG. I, but showing the part in a different position;

FIG. 6 is another longitudinal section similar to FIGS. I and 5, but showing the parts in a still different positron;

FIG. 7 is a vertical sectional view similar to FIG. I, but showing a modified embodiment of my gate operating mechanism; and

FIG. 8 is a cross section on line VIII-VIII of FIG. 7.

FIGS. I, 3 and 4 show a portion of a conventional bottom-pour vessel for handling liquid metals, for example, a ladle, a tundish or a degassing vessel. The vessel includes a metal shell II), a refractory lining I2, and a pouring nozzle 13 extending through the shell and lining. A mounting plate 14 is fixed to the underside of the vessel wall with studs I5 which project from the shell III (FIGS. 3 and 4). A pair of parallel rails I6 are fixed to the mounting plate I4 with bolts I7 (FIG. 4). The mounting plate surrounds the nozzle 13, and the rails are situated at oppoiste sides of the nozzle. The rails have shoulders I8 which support a refractory top plate I9 situated immediately beneath the nozzle I3. The top plate I9 has an orifice 20 which forms a continuation of the nozzle opening.

The rails I6 have opposed inwardly directed flanges 23 along their lower edges. A blank gate 24 or an orifice gate 25 may be received and temporarily supported on flanges 23 for sliding movement along the rails. Either gate can be positioned in line with the nozzle selectively to close the nozzle or permit pouring therethrough. FIGS. I, 2 and 3 show the blank positioned under the nozzle to close off flow, and the nozzle gate temporarily supported to the left of the blank. Two rows of rocker arms 26 are pivoted to the rails I6 on pins 27 at opposite sides of the nozzle. The rails have respective vertical bores 28 above the outboard ends of the rocker arms. Compression springs 29 are housed within bores 28and urge the outboard ends of the rocker arms downwardly, whereby the inboard ends bear upwardly against the gate and urge it into liquidtight engagement with the top plate I9. The upper faces of rails I6 carry cover plates 30 which retain the springs within the bores (FIG. 3). The lower faces of the rails carry heat and spatter shields 31. Air inlet pipes 32 are connected to the rails for supplying air to cool the springs (FIG. 2). The ends of rails I6 at the right, as viewed in FIGS. I and 2, carry a cross bar 33 on which I mount a fluid-pressure cylinder 34. The cylinder is located at the side of the vessel remote from the operators normal station. In this embodiment the rails I6 and cross bar 33 together form a frame which supports the other parts of the mechanism. The cylinder has a reciprocable piston rod 35, to the end of which I attach a ram block 36. The structure of the rails, gates, rocker arms, springs, and cylinder per se is similar to that commonly used in this art.

In accordance with the present invention, I attach a pair of pull links 40 to opposite sides of the ram block 36. As best shown in FIG. 2, these links extend along the side edges of gates 24 and 25, between the gates and rails I6. The ends of the links carry gate-pulling means in the form of a pivoted latch 4I. I pivot a retracting yoke 42 to the rails above gate 25. The end face of latch 41 has a socket 43 adapted to receive the yoke as shown in FIG. I.

In operation, the operator first manually loads a blank gate 24 on the flanges 23 of rails I6. While he loads each gate, the piston rod 35 is fully projected from cylinder 24, and latch 4I engages yoke 42, whereby the latch and yoke occupy the raised position shown in FIG. I. Thus the ends of the rails are free of obstructions which would interfere with loading. After loading the blank gate, the operator retracts the piston rod, whereupon latch 41 drops out of engagement with yoke 42 into a position behind the gate, as shown in FIG. 5. On continued retraction of the piston rod, the latch pulls the blank gate along the rails until it is aligned with the nozzle 13. Next the operator projects the piston rod and loads the orifice gate 25 into the space between the latch and the blank gate. Later, when pouring is to begin, the operator again retracts the piston rod and the atch pulls the two gates along the rails until the orifice gate is aligned with the nozzle. The blank continues to occupy the space between the orifice gate and the ram block 36, but is displaced along the rails toward the propelling means. To discontinue pouring, the operator projects the piston rod, the ram block pushes both gates to the left, and the parts return to the position shown in FIG. 1. The socket 43 of the latch automatically receives the yoke 42, and the latch and yoke pivot upwardly out of the way. If there is need, the operator can freely removed and replace the orifice gate, while the original blank remains in place.

To remove the blank gate 24, the operator removes the orifice gate 25 as already described and retracts the piston rod 35. Latch 41 moves into a position near the edge of the blank as shown in FIG. 6, leaving an open space between the blank and the ram block 36. The operator inserts a dummy gate 44 in this space and projects the piston rod. The ram block 36 pushes the dummy gate and blank to the left where the blank can be manually lifted from the rails. The latch 41 and yoke 42 move to their raised position as before. Preferably I equip the dummy gate with a handle 45 extending from its underside to facilitate manipulating it.

FIGS. '7 and 8 show a modified eembodiment of my gate-operating mechanism in which I have eliminated the latch used in the embodiment shown in FIGS. 1 to 6, and in which the displaced gate drops away. The modified embodiment is shown installed on a vessel which includes a metal shell 10a, a refractory lining 12a, a pouring nozzle 13a, and a mounting plate 14a. These parts are similar to the corresponding parts in the embodiment already described, except that the nozzle projects farther below the vessel bottom to provide more clearance for insertion of gates, as hereinafter explained.

The modified gate-operating mechanism includes a frame 50 attached to the mounting plate 14a with support pins 51 which extend through aligned holes in the frame and mounting plate. A stationary refractory top plate 19a removably rests in a recess in the upper face of the frame. The top plate has an orifice 20a which forms a continuation of the nozzle opening. A gate a is slidably supported under the top plate on two rows of rocker arms 26a at the inboard ends of the latter. The gate may be either a nozzle gate, as illustrated, to permit material to discharge through the nozzle 13a or a blank to prevent such discharge. Whenever the outlet is to be opened or closed, one type of gate is replaced by the other, as already described.

As shown in FIG. 8, each row of rocker anns 26a is pivoted to frame 50 on a respective pivot pin 27a. Spring housings 52 are mounted within the frame along opposite sides of the gate and each contains a respective compression spring 29a and a plunger 53 above the outboard end of a different rocker arm. Retaining plugs 54 are threadedly engaged with the upper ends of the spring housings. Springs 29a bear downwardly against the outboard ends of the rocket arms, while the inboard ends press the gate 250 firmly against the top plate 19a. The mounting palte 14a has air ducts 55 above the spring housing 52. The mounting plate carries downwardly directed nozzles 56 leading from the ducts. The retainer plugs have bores 57 affording communication between the nozzles and the interior of the spring housings. Air is blown into the spring housings via the ducts, nozzles and bores to prevent the springs from overheat- Frame 50 carries a double-acting fluid pressure cylinder 34a which contains a reciprocable piston and piston rod 35a. The end of the piston rod carries a ram block 36a. Links or pull rods 40a are attached to opposite sides of the ram block and extend through bores 58 in the spring housing 52. Alternatively the pull rods 40a could extend outside the gate as shown in FIG. 4. Gatepulling means in the form of a puller block 59 is attached to the ends of rods 40a remote from the ram block. Frame 50 carries a pair of fixed rests 60 at the end of the respective rows of rocker arms 26a nearer the puller block 59. The puller block has a ledge 61, the upper face of which is substantially coplanar with the upper gate-engaging faces of rocker arms 26a and rests 60.

When the piston rod 35a is fully extended as shown in FIG. 7, the operator can insert a new gate (shown in phantom from above into the space between the preceding gate 25a and the puller block 59, where it is supported temporarily on the rests 60 and ledge 61. Cylinder 34a then may be operated to retract its piston rod 35a and pull the new gate into the position originally occupied by the old, which is displaced simultaneously toward the propelling means and drops from the vessel. The additional clearance between the puller block and the vessel bottom makes it possible to insert gates by this procedure without need for a pivoted latch.

The operator normally is stationed on the same side of the vessel as the latch 41 or the puller block 59. Hence with either embodiment of my invention he can insert a new gate into the mechanism with little inconvenience. Since the cylinder 34 or 34a is at the other side of the vessel, it is not an obstacle. The first embodiment has the advantage of a reciprocating gate in that it enables the outlet to be opened or closed without installing a new gate for each operation. In particular the orifice gate can be removed and replaced without disturbing the blank. It is apparent that a similar advantage can be obtained in the modified embodiment by adding rails to the frame spanning the space between the rocker arms and cylinder as in the first embodiment. Conveniently the mechanism can be manufactured as an assembly ready for installaion on a vessel.

I claim:

1. In an assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising:

a frame adapted to be fixed to the vessel;

two rows of rocker arms pivoted to opposite sides of said frame for slidably supporting a gate at their inboard ends in alignment with the nozzle;

spring means housed in said frame and acting against said rocker arms at their outboard ends; reciprocable propelling means mounted on said frame at one end thereof and a block operatively connected with said propelling means;

the combination therewith of an improved gate operating mechanism comprising:

pull members attached to said block and extending above said rocker arms alongside the space occupied by a gate supported thereon;

gate-pulling means carried by said pull members and spaced from said rocker arms; and gate-receiving means carried by said frame in the space between said rocker arms and said gatepulling means for temporarily supporting gates;

said gate-pulling means being freely engageable with one end of a gate supported on said gate-receiving means for pulling this gate into a position in which it is supported on said rocker arms and displacing a preceding gate from said rocker arms toward said propelling means;

said gate-receiving means being accessible for having gates loaded thereon at the end of said frame remote from said propelling means.

2. The combination, with a bottom-pour vessel having a nozzle in its bottom wall, of an assembly attached to the vessel for controlling flow of material through said nozzle, said assembly being constructed as defined in claim ll.

' 3. A combination as defined in claim 2 in which said vessel is a refractory-lined tundish for teeming molten metal.

4. A mechanism as defined in claim 1 in which said frame includes a pair of spaced parallel rails, and said gate-receiving means are flanges integral with said rails.

5. A mechanism as defined in claim 4 in which said gate-pulling means includes a latch pivotally related to said pull members, and comprising in addition means mounted on said rails and engageable with said latch for automatically moving it between a position for engaging a gate and a position in which said rails are unobstructed to permit a gate to be loaded thereon.

6. A mechanism as defined in claim 4 in which said rails have flanges between said rocker arms and said propelling means for receiving a gate displaced from said rocker arms.

'7. A mechanism as defined in claim 11 in which said gate-pulling means includes a puller block fixed to said pull members, and said gate receiving means includes a rest carried by said frame and a ledge on said puller block.

3. An assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising a mounting plate, a pair of rails fixed to said plate and adapted to provide slidable support for separate blank and orifice gates, reciprocable propelling means fixed at one end of said rails, a ram block operatively connected with said propelling means and freely engageable with one end of a gate for pushing gates in one direction along said rails, pull members attached to said block and extending alongside the space occupied by gates supported on said rails, and means carried by said pull members spaced from said block and freely engageable with one end of another gate for pulling a pair of gates along said rails in the direction opposite said one direction, said rails being accessible at a location between said last named means and said nozzle for loading gates thereon in a position to be engaged both by said block and by themeans carried by said pull members.

9 The combination, with a bottom-pour vessel having a nozzle in its bottom call, and blank and orifice gates either of which can be positioned in line with said nozzle selectively to close the nozzle and permit pouring therethrough, of an operating mechanism for said gates, said mechanism comprising a pair of rails mounted on the bottom of said vessel, said gates being slidably supported on said rails, reciprocable gatepropelling means mounted on the bottom of said vessel, a ram block operatively connected with said gatepropelling means and freely engageable with one end of one gate for pushing said gates along said rails in one direction with respect to said nozzle, pull members attached to said block and extending alongside said gates, and means carried by said pull members spaced from said block and freely engageable with one end of the other gate for pulling said gates along said rails in the opposite direction said one direction with respect to said nozzle, said rails being accessible between said last named means and said nozzle for loading gates thereon in a position to be engaged both by said block and by the means carried by said pull members.

10. An assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising a mounting plate, a pair of rails fixed to said plate and adapted to provide slidable support for separate blank and orifice fates, reciprocable propelling means fixed at one end of said rails, ram means operatively connected with said propelling means and freely engageable with one end of a gate for pushing gates in one direction along said rails, and gate-pulling means attached to said ram means and extending along said rails, said gate-pulling means including a latch freely engageable with one end of another gate for pulling the gates along said rails in the opposite direction, said latch being disengageable from the latter gate to permit gates to be loaded and removed from one end of said rails.

Ill. An assembly as defined in claim 10 in which the ends of said rails opposite said propelling means normally are unobstructed.

12. An assembly as defined in claim 11 in which said mechanism further comprises means automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram means in said first-named direction.

113. The combination with a bottom-pour vessel having a nozzle in its bottom wall, and blank and orifice gates either of which can be positioned in line with said nozzle selectively to close the nozzle or permit pouring therethrough, of an operating mechanism for said gates, said mechanism comprising a pair of rails mounted on the bottom of said vessel, said gates being slidably supported on said rails, reciprocable gatepropelling means mounted at the bottom of said vessel, ram means operatively connected with said gatepropelling means and freely engageable with one end of one gate for pushing said gates along said rails in one direction with respect to said nozzle, and gate-pulling means attached to said ram means, said gate-pulling means including a latch freely engageable with one end of the other gate for pulling said gates along said rails in the opposite direction with respect to said nozzle, said latch being disengageable from the latter gate to permit gates to be loaded and removed from one end of said rails.

14. A combination as defined in claim 3 in which said gate-propelling means is mounted at one end of said rails, and the other ends of said rails normally are unobstructed.

15. A combination as defined in claim 14 in which said mechanism further comprises means automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram means in said first-named direction.

16. A combination as defined in claim 13 in which said gate-pulling means includes a pair of links attached to opposite sides of said ram means and extending along the side edges of said gates between the gates and rails, and said latch is pivoted to said links, and said mechanism further comprises means pivoted to said rails and engageable with said latch for automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram in said first-named direction.

17. A combination as defined in claim 16 in which the means pivoted to said rails includes a retracting yoke and said latch has a socket receiving said yoke.

18. An assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising a frame, spring-pressed means carried by said frame for above to enable a gate to be loaded thereon, said puller block being adapted to pull a gate from said gatereceiving means to said spring-pressed means and displace a preceding gate from the latter.

19. An assembly as defined in claim 18 in which said gate-receiving means is carried in part by said frame and in part by said puller block.

20. An assembly as defined in claim 18 in which said gate-receiving means includes rests carried by said frame adjacent said spring-pressed means, and a ledge carried by said puller block, the upper faces of said rests and said ledge being substantially coplanar with said spring-pressed means.

21. The combination with a bottom-pour vessel having a nozzle in its bottom wall, of an assembly attached to the vessel for controlling flow of material through said nozzle, said assembly being constructed as defined in claim 18.

22. A method of controlling flow of liquid through a nozzle in a bottom pour vessel, said method comprising positioning a blank gate in line with the nozzle initially to close off flow, pulling with an engaging means a separate orifice gate into line with the nozzle to permit flow through the nozzle and orifice gate, said orifice gate displacing said blank gate toward the propulsion source as said engaging means effects said pulling, and pushing the two gates in the direction opposite the direction in which they were pulled to close off flow and to disengage said engaging means from said on'fice gate with the same motion with which the gates are pushed in the latter direction, w hgr eby said orifice gate canbe replaced.

23. A method as defined in claim 22 in which said gates are freely loaded and removed at a location remote from the propulsion source.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,Y79 ,l .2l Dated December 18, 1973 Inventor(s) Earl P. Shapland, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet item [75] Earle P. Shapland, Jr

should read Earl P. Shapland, Jr.

Column 1, line 05, "part" should read harts Column 3, line 10, atch" should read latch line 20, "removed should read remove line 31 "eemcodiment" should read embodiment-- Column 1 line 3, palte should read plate 0011mm 6, claim 9, line 2, "eall" should read wall claim 9, line 18, "opposite direction" should read direction opposite claim 10, line 28, "fates" should read gates Column 7, claim 111,, line 1, "3 should read 13 Signed and sealed this 7th day of May 19714..

(SEAL) I Attest:

EDWARD ILFIETCI-IERJR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P0405) uscoMM-oc scan-pea y is. GOVERNMENT PRINTING OFFICE '99 0-388-331. 

1. In an assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising: a frame adapted to be fixed to the vessel; two rows of rocker arms pivoted to opposite sides of said frame for slidably supporting a gate at their inboard ends in alignment with the nozzle; spring means housed in said frame and acting against said rocker arms at their outboard ends; reciprocable propelling means mounted on said frame at one end thereof and a block operatively connected with said propelling means; the combination therewith of an improved gate operating mechanism comprising: pull members attached to said block and extending above said rocker arms alongside the space occupied by a gate supported thereon; gate-pulling means carried by said pull members and spaced from said rocker arms; and gate-receiving means carried by said frame in the space between said rocker arms and said gate-pulling means for temporarily suPporting gates; said gate-pulling means being freely engageable with one end of a gate supported on said gate-receiving means for pulling this gate into a position in which it is supported on said rocker arms and displacing a preceding gate from said rocker arms toward said propelling means; said gate-receiving means being accessible for having gates loaded thereon at the end of said frame remote from said propelling means.
 2. The combination, with a bottom-pour vessel having a nozzle in its bottom wall, of an assembly attached to the vessel for controlling flow of material through said nozzle, said assembly being constructed as defined in claim
 1. 3. A combination as defined in claim 2 in which said vessel is a refractory-lined tundish for teeming molten metal.
 4. A mechanism as defined in claim 1 in which said frame includes a pair of spaced parallel rails, and said gate-receiving means are flanges integral with said rails.
 5. A mechanism as defined in claim 4 in which said gate-pulling means includes a latch pivotally related to said pull members, and comprising in addition means mounted on said rails and engageable with said latch for automatically moving it between a position for engaging a gate and a position in which said rails are unobstructed to permit a gate to be loaded thereon.
 6. A mechanism as defined in claim 4 in which said rails have flanges between said rocker arms and said propelling means for receiving a gate displaced from said rocker arms.
 7. A mechanism as defined in claim 1 in which said gate-pulling means includes a puller block fixed to said pull members, and said gate receiving means includes a rest carried by said frame and a ledge on said puller block.
 8. An assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising a mounting plate, a pair of rails fixed to said plate and adapted to provide slidable support for separate blank and orifice gates, reciprocable propelling means fixed at one end of said rails, a ram block operatively connected with said propelling means and freely engageable with one end of a gate for pushing gates in one direction along said rails, pull members attached to said block and extending alongside the space occupied by gates supported on said rails, and means carried by said pull members spaced from said block and freely engageable with one end of another gate for pulling a pair of gates along said rails in the direction opposite side one direction, said rails being accessible at a location between said last named means and said nozzle for loading gates thereon in a position to be engaged both by said block and by the means carried by said pull members. 9 The combination, with a bottom-pour vessel having a nozzle in its bottom eall, and blank and orifice gates either of which can be positioned in line with said nozzle selectively to close the nozzle and permit pouring therethrough, of an operating mechanism for said gates, said mechanism comprising a pair of rails mounted on the bottom of said vessel, said gates being slidably supported on said rails, reciprocable gate-propelling means mounted on the bottom of said vessel, a ram block operatively connected with said gate-propelling means and freely engageable with one end of one gate for pushing said gates along said rails in one direction with respect to said nozzle, pull members attached to said block and extending alongside said gates, and means carried by said pull members spaced from said block and freely engageable with one end of the other gate for pulling said gates along said rails in the opposite direction said one direction with respect to said nozzle, said rails being accessible between said last named means and said nozzle for loading gates thereon in a position to be engaged both by said block and by the means carried by said pull members.
 10. An assembly for attachment to a bottom-pour vessel for controlling flow of liquId through a nozzle in the bottom wall of the vessel, said assembly comprising a mounting plate, a pair of rails fixed to said plate and adapted to provide slidable support for separate blank and orifice fates, reciprocable propelling means fixed at one end of said rails, ram means operatively connected with said propelling means and freely engageable with one end of a gate for pushing gates in one direction along said rails, and gate-pulling means attached to said ram means and extending along said rails, said gate-pulling means including a latch freely engageable with one end of another gate for pulling the gates along said rails in the opposite direction, said latch being disengageable from the latter gate to permit gates to be loaded and removed from one end of said rails.
 11. An assembly as defined in claim 10 in which the ends of said rails opposite said propelling means normally are unobstructed.
 12. An assembly as defined in claim 11 in which said mechanism further comprises means automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram means in said first-named direction.
 13. The combination with a bottom-pour vessel having a nozzle in its bottom wall, and blank and orifice gates either of which can be positioned in line with said nozzle selectively to close the nozzle or permit pouring therethrough, of an operating mechanism for said gates, said mechanism comprising a pair of rails mounted on the bottom of said vessel, said gates being slidably supported on said rails, reciprocable gate-propelling means mounted at the bottom of said vessel, ram means operatively connected with said gate-propelling means and freely engageable with one end of one gate for pushing said gates along said rails in one direction with respect to said nozzle, and gate-pulling means attached to said ram means, said gate-pulling means including a latch freely engageable with one end of the other gate for pulling said gates along said rails in the opposite direction with respect to said nozzle, said latch being disengageable from the latter gate to permit gates to be loaded and removed from one end of said rails.
 14. A combination as defined in claim 3 in which said gate-propelling means is mounted at one end of said rails, and the other ends of said rails normally are unobstructed.
 15. A combination as defined in claim 14 in which said mechanism further comprises means automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram means in said first-named direction.
 16. A combination as defined in claim 13 in which said gate-pulling means includes a pair of links attached to opposite sides of said ram means and extending along the side edges of said gates between the gates and rails, and said latch is pivoted to said links, and said mechanism further comprises means pivoted to said rails and engageable with said latch for automatically moving said latch to a position out of the way of loading and removing gates when said propelling means moves said ram in said first-named direction.
 17. A combination as defined in claim 16 in which the means pivoted to said rails includes a retracting yoke and said latch has a socket receiving said yoke.
 18. An assembly for attachment to a bottom-pour vessel for controlling flow of liquid through a nozzle in the bottom wall of the vessel, said assembly comprising a frame, spring-pressed means carried by said frame for slidably supporting a gate in alignment with the nozzle, reciprocable propelling means carried by said frame at one end thereof, a ram block operatively connected with said propelling means, pull links carried by said ram block and extending past said spring-pressed means, a puller block carried by said links and spaced from said spring-pressed means, and gate-receiving means in the space between said puller block and said spring-pressed means for temporarily supporting a gate, said gAte-receiving means being accessible from above to enable a gate to be loaded thereon, said puller block being adapted to pull a gate from said gate-receiving means to said spring-pressed means and displace a preceding gate from the latter.
 19. An assembly as defined in claim 18 in which said gate-receiving means is carried in part by said frame and in part by said puller block.
 20. An assembly as defined in claim 18 in which said gate-receiving means includes rests carried by said frame adjacent said spring-pressed means, and a ledge carried by said puller block, the upper faces of said rests and said ledge being substantially coplanar with said spring-pressed means.
 21. The combination with a bottom-pour vessel having a nozzle in its bottom wall, of an assembly attached to the vessel for controlling flow of material through said nozzle, said assembly being constructed as defined in claim
 18. 22. A method of controlling flow of liquid through a nozzle in a bottom-pour vessel, said method comprising positioning a blank gate in line with the nozzle initially to close off flow, pulling a separate orifice gate into line with the nozzle to permit flow with the orifice gate by displacing the blank gate with an engaging means toward the propulsion source affecting said pulling, and pushing the two gates in the direction opposite the direction of said pulling step to again close off flow and to disengage said engaging means from said orifice gate with the same motion with which the gates are pushed in the latter direction to allow replacement of said orifice gate.
 23. A method as defined in claim 22 in which said gates are freely loaded and removed at a location remote from the propulsion source. 